Thousands of people gathered for a rally in central London to protest the rise in anti-Semitism in Britain.

The rally Sunday outside the Royal Courts of Justice was organized by the Campaign Against Anti-Semitism, a grassroots group formed in response to the rise in attacks against Jews in Britain and throughout Europe following the start of the Gaza conflict.

“I would never have believed a year ago I would be standing here expressing my deep concern about the rise of anti-Semitism in the UK,” Chief Rabbi Ephraim Mirvis said in an address to the crowd, the Jewish Chronicle reported. “We are right to be concerned. We see it, we hear it, and we feel it. It is there.”

The rabbi said he has received letters of support from private citizens as well as national leaders. “A threat to Jews is a threat to our society,” he said. “We are not alone.”

Signs in the crowd read: “Zero tolerance for anti-Semites” and “prosecute hate before it’s too late.”

Leaders of the Board of Deputies of British Jewry were jeered as they were introduced, amid shouts of “you’re not doing enough” and “resign.” The board backed the rally.

There were 240 anti-Semitic incidents in Britain in July, compared to 304 anti-Semitic incidents in the first six months of the year, according to the British anti-Semitism watchdog Community Security Trust.